1. Field of the Invention
The present invention relates to a backlight device that illuminates a transmissive liquid crystal panel, and a liquid crystal display device and an electronic apparatus including the backlight device.
2. Description of the Related Art
A liquid crystal display device optically displays, for example, a predetermined image by changing light transmittance as a result of changing the orientation of liquid crystal molecules by applying voltage when liquid crystals are provided between two transparent substrates. Since the liquid crystals, themselves, are not light emitters, the liquid crystal display device is provided with, for example, a backlight device that illuminates a back surface side of a liquid crystal panel with illumination light from a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED).
In the backlight device, the liquid crystal panel is illuminated from its back surface side with illumination light from a light source including a plurality of light-emitting diodes, and each optical sheet performs optical operations on the illumination light, such as diffusing, reflecting, and guiding the illumination light. As a result, the liquid crystal panel is uniformly and stably illuminated with the illumination light over its entire surface.
For example, in a backlight device disclosed in Japanese Unexamined Patent Application Publication No. 2005-352427 (Patent Document 1), each light source substrate is mounted to one surface of a back chassis, which is a basic structure of the backlight device, and a reflecting sheet is provided so as to face and so as to be separated from the back chassis. Therefore, the backlight device disclosed in Patent Document 1 has a double bottom structure formed by the back chassis and the reflecting sheet, thereby making the structure complicated and increasing the weight of the backlight device.
In the backlight device disclosed in Patent Document 1, the reflecting sheet exists directly above a first surface of each light source substrate, and a heat plate is mounted to a second surface of each light source substrate. Therefore, in a limited narrow space between the first surface of each light source substrate and the facing reflecting sheet provided directly above the first surface of each light source substrate, a plurality of light-emitting diodes, a wiring pattern, used to wire the light-emitting diodes in series, and wiring parts, such as light source harnesses or connectors, are mounted to the first surfaces of the light source substrates, thereby limiting the degree of design freedom.
In addition, in the backlight device disclosed in Patent Document 1, the light source substrates are cooled in the following manner. Heat generated by the light-emitting diodes is moved to a heat sink through a heat pipe by the heat plate, which is mounted to each of the light source substrates, to cool the generated heat by, for example, a cooling fan. However, since the cooling method depends upon heat conduction, through, for example, the heat plate, its cooling efficiency depends upon, for example, the method of mounting the light source substrates. Further, since the light source substrates, the heat plate, the heat pipe, the heat sink, etc. are formed using aluminum material, they are heavy, difficult to process, and are expensive.